Malignant adenomyoepithelioma of the breast: a rare case report and literature review

Adenomyoepithelioma (AME) of the breast is a rare biphasic tumor composed of epithelial and myoepithelial elements, with malignant transformation being exceptionally uncommon. We report a case of pure malignant adenomyoepithelioma (M-AME) in a 51-year-old woman who presented with a gradually enlarging left breast mass. Imaging revealed a 3.6 cm lesion, and core biopsy showed biphasic proliferation with myoepithelial atypia and high mitotic activity. Wide local excision with oncoplastic reduction achieved negative margins, and histopathology confirmed pure M-AME (pT2 pN0), triple-negative for estrogen, progesterone, and Human Epidermal growth factor Receptor 2, with a Ki-67 index of 35%-40%. The patient received adjuvant radiotherapy and remains disease-free at 1 year. This case highlights the diagnostic challenges of M-AME, underscores the importance of immunohistochemistry and complete excision with negative margins, and adds to the limited literature on this exceptionally rare breast neoplasm.